REPORT ON THE KERATOSA. 35 



have only to summarise the foregoing observations. I do it in the following words : — 

 ivith the exception of the genera Darwinella, lanthella, and Psammopemma, all genera 

 are devoid of any properties separating them absolutely from one another. 



The further conclusions deducible from this statement will be given in the last 

 part of this Report, for they will only be instructive when we shall have learned the 

 properties used at the present time in order to distinguish and characterise the species. 

 An abstract discussion of all such properties would lead me too far ; it is besides unneces- 

 sary, since the following chapter, devoted to the description of the forms brought home by 

 the Challenger Expedition, may serve as a better illustration of them than any however 

 detailed but abstract discussions. Some remarks with respect to the external character 

 of the following descriptions : as in my memoir on the Challeilger Calcarea, the reader 

 will not find any specific diagnoses ; I must confess I regard them in most cases as a loss 

 of space and time, and altogether superfluous, especially as nearly every species in the 

 Challenger Collection of Keratosa is represented by a single specimen only, so that the 

 tendency to vary could not be made out. As to this question in general, I refer the 

 reader to the extremely instructive paper of Heincke on the varieties of the herring ^ ; on 

 the other hand, I invite him to peruse the diagnoses of Calcarea given by Haeekel in 

 his " Kalkschwamme " for every species. Would he receive any idea of the animal from 

 a similar diagnostic description ? I think not. And this with respect to Sponges, the 

 geometrical properties of whose spicules present far more tenable systematic distinctions 

 than is the case with regard to the Keratosa. As to those described in this paper, I 

 regard their entire descriptions as diagnoses, and end this chapter with the following 

 observations of a practical nature. 



All the specimens in the collection not devoid of soft parts have been examined with 

 regard to their canal system and skeleton. The skeletal fibres have been examined 

 both in spirit and mounted in Canada balsam, after previous treatment with ammonia, 

 in order to remove the soft parts. These latter have been examined in sections stained 

 in different ways by different staining fluids ; for it must be stated that while for 

 the Calcarea no other staining fluid but picro-carmine is to be recommended, the matter 

 is quite difterent with regard to the Keratosa, so that in each case the investigator must 

 proceed experimentally. 



1 Die Varietaten ties Herings, Berlin, 1877. 



